In the words of a famous PUA, men are here for one reason....Survival. We survive by mating with women, and women replicate. Survive and replicate.
If you want to deduce it to the simplest levels, men are here to plant their seed in as many women. And women are here to have as many babies to keep the human race alive.
All other things that follow, such as having too many kids and struggling through life and finances, population control, shortages on many of the natural supplies in the world....can stem from these two actions; survival and replication.